Building radar aerials or antennas for transmission/reception of radar signals within two separate frequency bands is already known.
(a) In a known embodiment of the radar aerial two entirely separate aerial elements are arranged for both frequency bands.
(b) In another known embodiment, two separate feeder systems for the two frequency bands are arranged, these systems having a common reflector system and being placed in the vicinity of each other
(c) In a further embodiment, two feeder systems are used for different frequency bands located at two different focal points in a Cassegrain aerial system, which will be described in detail in conjunction with FIG. 1 on the accompanying drawing.
The disadvantage with the embodiment according to (a) is that the antenna system requires at least twice as much space as when only one frequency band were to be transmitted or received.
The disadvantage with the embodiment according to (b) is that lobe directions are obtained which do not coincide for both frequency bands. Furthermore, both the feeders cannot be placed in focus, and one or both must be defocused, which results in somewhat deteriorated performance.
In the embodiment according to (c) the greatest disadvantage is that one of the feeders (usually the one for the higher frequency) must be placed in the outer focal point. Thus the depth of the aerial increases considerably, at the same time as the feeder, its support and supply lines decrease the radiation surface of the aerial. There are also losses from the long lines to the feeder.